Method and device for controlling an exhaust gas aftertreatment system

ABSTRACT

A method and a device are described for controlling an exhaust gas aftertreatment system, in particular for an internal combustion engine. A first quantity (SIMP), based on first characteristic operating quantities, which characterizes the amount of substances supplied to the exhaust gas aftertreatment system is determined in a first operating state. A second quantity (SIMR), based on second characteristic operating quantities, which characterizes the amount of substances removed from the exhaust gas aftertreatment system is determined in a second operating state. The first quantity and the second quantity are compared for error detection.

BACKGROUND INFORMATION

[0001] The present invention relates to a method and a device for controlling an exhaust gas aftertreatment system, in particular of an internal combustion engine, according to the preambles of the independent claims.

[0002] A method and a device for controlling an internal combustion engine having an exhaust gas aftertreatment system are known from German Patent DE 199 06 287. As described therein, the exhaust gas aftertreatment system has a particle filter which is used in particular in direct injection internal combustion engines. The loading of the particle filter is detected as a state quantity. When specific values are exceeded, the device initiates a special operating state in which the particle filter is regenerated using suitable measures.

[0003] Frequently, the differential pressure, i.e., the pressure difference between the inlet and the outlet of the filter, is evaluated to detect the load state. When the particle filter is damaged, such as when a tear is present, the load state of the filter can no longer be reliably detected via the differential pressure, since a portion of the exhaust gas flows through the tear. In addition, particles would be emitted to the environment, which could result in exceedance of emission standards.

ADVANTAGES OF THE INVENTION

[0004] The exhaust gas aftertreatment system may be easily and reliably monitored by determining a second quantity, based on second characteristic operating quantities, which characterizes the amount of substances removed from the exhaust gas aftertreatment system in a second operating state in which the particle filter is regenerated, and by comparing this second quantity to the first quantity, which characterizes the amount of substances supplied to the exhaust gas aftertreatment system. Preferably, errors are detected when the two quantities deviate significantly from one another.

[0005] It is preferable to use the method for particle filters, the amount of particles accumulating in the particle filter during normal operation being compared to the amount of particles combusted during regeneration.

[0006] The amount of substances removed may be determined in a particularly simple and reliable manner by evaluating the temperature upstream and downstream from the particle filter. During regeneration of the particle filter, the reaction of the particles results in a temperature increase, which may be detected relatively easily using sensors upstream and downstream from the sensor. A defect in the filter may be reliably detected based on the comparison of these two quantities.

[0007] A signal which characterizes the amount of oxygen in the exhaust gas has proven to be particularly advantageous as the second quantity. To this end, the oxygen content in the exhaust gas upstream and downstream from the filter is detected. A conclusion as to the amount of regenerated particles is made based on the mass of the reacted oxygen.

DRAWING

[0008] The present invention is explained in the following description with reference to the embodiments illustrated in the drawing.

[0009]FIG. 1 shows a block diagram of the control according to the present invention, and

[0010]FIG. 2 shows a flow diagram which illustrates the method according to the present invention.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

[0011]FIG. 1 illustrates the essential elements of an exhaust gas aftertreatment system of an internal combustion engine. The internal combustion engine is indicated by reference number 100. Fresh air is supplied to the internal combustion engine via a fresh air line 105. The exhaust gas from internal combustion engine 100 is discharged through an exhaust gas line 110 to the environment. An exhaust gas aftertreatment system 115 is situated in the exhaust gas line. The exhaust gas aftertreatment system may be a catalyst and/or a particle filter. In addition, a plurality of catalysts for different contaminants, or combinations of at least one catalyst and one particle filter may be provided.

[0012] Furthermore, a control device 170 is provided which has at least one engine control device 175 and one exhaust gas aftertreatment control device 172. Engine control device 175 sends control signals to a fuel metering system 180. Exhaust gas aftertreatment control device 172 sends signals to engine control device 175 and, in one embodiment, to an actuating element 182 situated in the exhaust gas line upstream from the exhaust gas aftertreatment system or in the exhaust gas aftertreatment system.

[0013] In addition, various sensors are provided which supply signals to the exhaust gas aftertreatment control device and the engine control device. Thus, at least one first sensor 194 is provided that delivers signals which characterize the state of the air supplied to the internal combustion engine. A second sensor 177 delivers signals which characterize the state of fuel metering system 180. At least one third sensor 191 delivers signals which characterize the state of the exhaust gas upstream from the exhaust gas aftertreatment system. At least one fourth sensor 193 delivers signals which characterize the state of exhaust gas aftertreatment system 115. In addition, at least one sensor 192 delivers signals which characterize the state of the exhaust gas downstream from the exhaust gas aftertreatment system. It is preferable to use sensors which detect the temperature values and/or pressure values. Furthermore, sensors may also be used which characterize the chemical composition of the exhaust gas and/or fresh air. These sensors are lambda sensors, NOx sensors, or HC sensors, for example.

[0014] Output signals are preferably sent to exhaust gas aftertreatment control device 172 from first sensor 194, third sensor 191, fourth sensor 193, and fifth sensor 192. Output signals are preferably sent to engine control device 175 from second sensor 177. Additional sensors, not shown, may also be provided which characterize a signal according to the driver's intent, or other environmental or engine operating states.

[0015] It is particularly advantageous if the engine control device and the exhaust gas aftertreatment control device form a structural entity. Alternatively, the engine control device and the exhaust gas aftertreatment control device may be designed as two control devices which are spatially separated from one another.

[0016] The method according to the present invention is described hereinafter using the example of a particle filter which is used in particular in direct injection internal combustion engines. The method according to the present invention is not limited to this application, however, and may also be used in other internal combustion engines having an exhaust gas aftertreatment system. In particular, the method according to the present invention may be used in exhaust gas aftertreatment systems in which a catalyst and a particle filter are combined. Furthermore, the method according to the present invention may be used in systems which are only equipped with a catalyst.

[0017] Based on the sensor signals which are present, engine control 175 calculates control signals for sending to fuel metering system 180. The fuel metering system then meters the corresponding amount of fuel to internal combustion engine 100. Particles may be formed in the exhaust gas during combustion. These particles are absorbed by the particle filter in exhaust gas aftertreatment system 115. Corresponding amounts of particles accumulate in particle filter 115 during operation. This results in impaired functioning of the particle filter and/or the internal combustion engine. For this reason, a regeneration process is initiated at specific intervals or when the particle filter has reached a specific load state. This regeneration may also be described as a special operation.

[0018] The load state is detected based on various sensor signals, for example. Thus, on the one hand it is possible to evaluate the differential pressure between the inlet and the outlet of particle filter 115. On the other, it is possible to determine the load state based on various temperature values and/or pressure values. In addition, other quantities may be used for calculating or simulating the load state. One appropriate method is known from German Patent DE 199 06 287, for example.

[0019] When the exhaust gas aftertreatment control device detects that the particle filter has reached a specific load state, regeneration is initialized. Various options are available for regenerating the particle filter. For one, certain substances may be supplied to the exhaust gas via actuating element 182 which then bring about a corresponding reaction in exhaust gas aftertreatment system 115. These additionally metered substances cause, among other effects, a temperature increase and/or oxidation of particles in the particle filter. Thus, for example, fuel substances and/or oxidation agents may be supplied via actuating element 182.

[0020] In one embodiment of the present invention, an appropriate signal may be transmitted to engine control device 175, which carries out what is known as post-injection. Using post-injection, it is possible to introduce hydrocarbons into the exhaust gas in a targeted manner, the hydrocarbons contributing to the regeneration of exhaust gas aftertreatment system 115 via an increase in temperature.

[0021] The load state is usually determined based on various quantities. The different states are detected by comparing to a threshold value, and the regeneration is initiated depending on the detected load state.

[0022] In a preferred embodiment of the present invention, sensor 191 is situated upstream from the particle filter as a first temperature sensor, and sensor 192 is situated downstream from the particle filter as second temperature sensor 192.

[0023] In another preferred embodiment of the present invention, sensor 191 is situated upstream from the particle filter as a first lambda sensor, and sensor 192 is situated downstream from the particle filter as second lambda sensor 192. Both lambda sensors deliver signals which characterize the oxygen concentration in the exhaust gas.

[0024] In one embodiment of the present invention, only one lambda sensor, which is situated downstream from the particle filter, is used. The oxygen concentration upstream from the particle filter is calculated based on various characteristic operating quantities or is read from a characteristic map. It is also possible to determine the oxygen concentration upstream from the particle filter based on the oxygen concentration before regeneration.

[0025]FIG. 2 illustrates the method according to the present invention for detecting a defect in the region of the exhaust gas aftertreatment system, with reference to a flow diagram. In a first operating state, which corresponds to normal operation of the internal combustion engine, the particles created are deposited in the particle filter. The amount of particles deposited is determined in a first step 200. This amount of deposited particles is referred to below as first quantity SIMP. This first quantity SIMP characterizes the amount of substances supplied to the exhaust gas aftertreatment system. For example, the load state of the particle filter may be used as the first quantity, or the first quantity may be determined based on the load state.

[0026] A subsequent query 210 checks whether a second operating state is present. If such a second operating state is not present, step 200 is repeated, and the first quantity is determined. If query 210 detects that a second operating state is present, step 220 is then carried out.

[0027] In the second operating state the particle filter is regenerated; i.e., the particles deposited in the filter are oxidized or combusted. The oxygen content of the exhaust gas is reduced and the temperature of the exhaust gas is increased. Based on one of these two quantities, a second quantity SIMR may be determined which characterizes the amount of substances removed from the exhaust gas aftertreatment system.

[0028] Thus, in step 220 the amount of heat released is calculated based on the difference in temperatures upstream and downstream from the particle filter. In the calculation of the amount of heat based on the temperature difference, in one particularly advantageous embodiment the heat capacity of the particle filter and/or the heat exchange, in particular the energy released to the environment, is taken into account. The heat capacity of the particle filter in particular results in dynamic effects which must be considered.

[0029] Based on various quantities, in particular the specific heat of the particles, the amount of particles combusted or removed from the filter during regeneration is determined based on the amount of heat.

[0030] In one embodiment of the method according to the present invention, the amount of particles combusted in step 220 is determined based on a quantity which characterizes the oxygen concentration in the exhaust gas. This calculation is preferably performed based on the decrease in the oxygen concentration in the particle filter. Based on the decrease in the oxygen concentration, the amount of reacted oxygen is determined, and from this value the amount of particles combusted is determined.

[0031] After regeneration has ended, query 230 checks whether quantities SIMR and SIMP are virtually the same. In other words, query 230 checks whether the first quantity and the second quantity deviate significantly from one another. This is the case when the difference between quantities SIMR and SIMP is larger than a threshold value. This threshold value is specified by the inaccuracy in determining quantities SIMR and SIMP. If the two quantities are virtually the same, step 200 is repeated. If the values deviate significantly from one another, errors are detected in step 240. Errors in the region of the particle filter are detected when the amount of particles supplied deviates significantly from the amount of particles combusted. 

What is claimed is:
 1. A method of controlling an exhaust gas aftertreatment system, in particular of an internal combustion engine, a first quantity (SIMP), based on first characteristic operating quantities, which characterizes the amount of substances supplied to the exhaust gas aftertreatment system being determined in a first operating state, wherein a second quantity (SIMR), based on second characteristic operating quantities, which characterizes the amount of substances removed from the exhaust gas aftertreatment system is determined in a second operating state; and the first quantity and the second quantity are compared for error detection.
 2. The method according to claim 1, wherein an error is detected when the two quantities deviate significantly from each another.
 3. The method according to claim 1 or 2, wherein the first quantity is the quantity of particles deposited in a particle filter.
 4. The method according to one of the preceding claims, wherein the second quantity is the quantity of particles removed during regeneration of the particle filter.
 5. The method according to one of the preceding claims, wherein an exhaust gas temperature and/or a quantity which characterizes the amount of oxygen in the exhaust gas are used to determine the second quantity.
 6. A device for controlling an exhaust gas aftertreatment system, in particular of an internal combustion engine, a first quantity (SIMP), based on first characteristic operating quantities, which characterizes the amount of substances supplied to the exhaust gas aftertreatment system being determined in a first operating state, wherein means are provided which determine a second quantity (SIMR), based on second characteristic operating quantities, which characterizes the amount of substances removed from the exhaust gas aftertreatment system in a second operating state; and which compare the first quantity and the second quantity for error detection. 